This application is a divisional application of U.S. patent application Ser. No. 10/880,972 (referred to as “the '972 application” and incorporated herein by reference), filed on Jun. 30, 2004, titled “ADJUSTING AD COSTS USING DOCUMENT PERFORMANCE OR DOCUMENT COLLECTION PERFORMANCE” and listing Brian AXE, Doug BEEFERMAN, Amit PATEL, Nathan STOLL, and Hal VARIAN as inventors.